Integrated circuits (ICs) which operate in two or more power supply voltages environment invariably require signals to interface between circuits supplied by different power supply voltages. One of the challenges in designing ICs is to accommodate several different power supply voltages on a single IC. Typically, an IC will have an internal or a core supply voltage used for powering the bulk of its internal circuitry. The voltage level of the internal supply is usually kept as low as possible in order to minimize power consumption and in some examples, to adhere to process node requirements. As IC fabrication processes continue to shrink the feature size of transistors, the ICs will continue to decrease in size, and therefore the allowable internal power supply voltage also decreases. For example, ICs fabricated using 90 nm processes can typically operate at approximately 1.2V, and future smaller processes can further lower the operating voltages.
For particular applications, an IC can be integrated with other ICs on an integrated circuit board (PCB). The ICs may have different operating voltages; therefore, it may be a requirement to use more than one power supply voltage setting in order to accommodate the various operating conditions of the ICs. For example, an IC may need to communicate with other elements and/or ICs in a system using an input/output (I/O) standard that requires a higher or a lower voltage level. In general, the low internal voltage of the IC may be electrically separated from the high I/O voltage. Therefore, the internal core circuits and I/O circuits may be coupled to their respective power supplies.
In another example, an IC may have multiple internal core circuits that may require separate power supply voltages in order to function properly. For instance, certain types of memory circuits require a high voltage (e.g., 12.0V). An IC which includes such memory circuits can use a separate high power supply voltage to operate the memory circuits properly. The circuits that use the higher power supply voltage and the circuits that use other supply voltages can communicate with each other using a level shifter. A level shifter is a type of circuit that translates logical signals of one voltage level to logical signals of another voltage level.
There are many other examples of applications that require the use of multiple voltage levels. In such applications, level shifters are necessary and may be used to communicate between two sections of an IC having different power supply voltages.
A problem with prior art level shifters is that their performance can be highly dependent on certain factors, including I/O signals voltage levels, power supplies voltage ranges, and the I/O operating frequencies. These factors may have a significant adverse effect on the performance of the level shifter, especially in a low voltage, and high-speed designs.
Therefore, the need exists for a high-speed, wide voltage range, and area efficient level-shifter that can tolerate variations in the power supply voltages and the I/O operating frequencies. In such instances, it would be advantageous to have a single level shifter circuit that is insensitive to the ranges of the power supply voltages, and the I/O operating frequencies, therefore maintaining optimized performance across wide range of applications and designs.